Biological Influences

Conditioning accounts for a lot of learning, both in humans and nonhuman
species. However, biological factors can limit the capacity for conditioning. Two
good examples of biological influences on conditioning are taste aversion and
instinctive drift.

Taste Aversion

Psychologist John Garcia and his colleagues found that
aversion to a particular taste is conditioned only by pairing the
taste (a conditioned stimulus) with nausea (an unconditioned stimulus). If taste
is paired with other unconditioned stimuli, conditioning doesn’t occur.

Similarly, nausea paired with most other conditioned stimuli doesn’t
produce aversion to those stimuli. Pairing taste and nausea, on the other hand,
produces conditioning very quickly, even with a delay of several hours between
the conditioned stimulus of the taste and the unconditioned stimulus of nausea.
This phenomenon is unusual, since normally classical conditioning occurs only
when the unconditioned stimulus immediately follows the conditioned stimulus.

Example:
Joe eats pepperoni pizza while watching a movie with his roommate, and three hours later, he becomes
nauseated. He may develop an aversion to pepperoni pizza, but he won’t develop an aversion to the movie he
was watching or to his roommate, even though they were also present at the same time as the pizza. Joe’s
roommate and the movie won’t become conditioned stimuli, but the pizza will. If, right after eating the pizza,
Joe gets a sharp pain in his elbow instead of nausea, it’s unlikely that he will develop an aversion to pizza
as a result. Unlike nausea, the pain won’t act as an unconditioned stimulus.

An Evolutionary Adaptation

The combination of taste and nausea seems to be a
special case. Researchers think that learning to quickly
associate taste and nausea is an evolutionary adaptation, since
this association helps people to know what foods to avoid in
order to survive.

Instinctive Drift

Instinctive drift is the tendency for conditioning to be
hindered by natural instincts. Two psychologists, Keller and Marian Breland,
were the first to describe instinctive drift. The Brelands found that through
operant conditioning, they could teach raccoons to put a coin in a box by using
food as a reinforcer. However, they couldn’t teach raccoons to put two coins in a box. If given two coins, raccoons just held on
to the coins and rubbed them together. Giving the raccoons two coins brought out
their instinctive food-washing behavior: raccoons instinctively rub edible
things together to clean them before eating them. Once the coins became
associated with food, it became impossible to train them to drop the coins into
the box.